EFFECTS OF SOIL STORAGE ON THE MICROBIAL COMMUNITY AND DEGRADATION OF METSULFURON-METHYL

Authors: Trabue, Steven - Steve; Palmquist, Debra; LYDICK, TARA - DELAWARE PUBLIC HEALTH LA; KOCH-SINGLES, SUZANNE - DUPONT CROP PROTECTION

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2006
Publication Date: 1/26/2006
Citation: Trabue, S.L., Palmquist, D.E., Lydick, T., Koch-Singles, S. Effects of soil storage on the microbial community and degradation of metsulfuron-methyl. Journal of Agricultural and Food Chemistry. 54(1):142-151.

Interpretive Summary: Soil metabolism studies for pesticides are used to evaluate how fast a compound degrades (breaks down), what are its major degradation products (metabolites), and what is its degradation pathway in soil. These studies are used to determine how a pesticide will behave in the environment and potential health risk to the environment this compound poses. Consequently, it is imperative that soils used in these studies have not been compromised during collection, processing and storage. The purpose of this study was to determine the effect storage has on soil microorganisms and what effect this had on the degradation of metsulfuron-methyl (herbicide). In this study, two soils (Trevino and Fargo) were collected from the field and used fresh (< 3 weeks old) or stored at 20 and 4 degrees C for 3 or 6 months. In both soils, there were more microorganisms in the fresh soils compared to soils stored for 6 months and the composition of the microorganisms changed between fresh soils and soils stored for over 6 months. The breakdown of metsulfuron-methyl changed with storage for both soils with faster breakdown occurring in fresh soil compared to stored soil. However, the degradation of metsulfuron-methyl was affected after only 3 months of storage. In addition, how the metsulfuron-methyl degraded also changed when comparing fresh soil to stored soils. Research results described in this report provides, academic scientist and regulatory scientists valuable information on the effects storage of soils has on a soil’s capacity to degrade pesticides, and demonstrate that storing soils should be kept if possible to a minimum and if storage must occur it should be for longer than 3 months.

Technical Abstract: The affect storage has on the microbial biomass in two soils (Trevino and Fargo) was compared to those soils capacity to degrade metsulfuron-methyl. Soils were collected from the field and used fresh (< 3 weeks old) or stored at 20 and 4 degrees C for 3 or 6 months. The phospholipid fatty acid content of the soils was used to monitor changes in the microbial biomass during storage and incubation in a flow-through apparatus. In both soils, [phenyl(U)-14C] metsulfuron-methyl was used to monitor changes in the route and rate of degradation along with monitoring [14C]carbon dioxide evolution (mineralization). Total microbial biomass in both soils were significantly reduced for soils incubated in the flow-through apparatus, while only the Trevino soil’s microbial biomass was significantly reduced as a result of storage. The microbial community of both soils was significantly different as a result of storage as shown by discriminate analysis. In both soils, degradation rate, pathway of degradation and mineralization of metsulfuron-methyl were significantly impacted by storage compared to fresh soil. The half-life of metsulfuron-methyl increased significantly (p < 0.05) in the Trevino soil from 45 days (fresh) to 63 days (stored soil), while in the Fargo soil half-lives increased significantly (p< 0.05) from 23 days (fresh) to 29 days (6 month stored soils). In both soils, mineralization of [phenyl(U)-14C] metsulfuron-methyl was significantly (p < 0.05) higher in fresh soils compared to stored soils. The degradation pathways of metsulfuron-methyl changed with storage as evidenced by the loss of one biologically derived degradate in stored soils compared to fresh soils.